[Bizgres-general] A bitmap index access method is available in bizgres CVS tip

[Jie Zhang]

> 
> I thought I would have a play (see below).

Thank you for testing.

> 
> What I am seeing is that vanilla Pg 8.1.1 with btree indexes on several
> low cardinality columns seems to be considerably faster than Bizgres
> with on-disk bitmaps (for my test case). I would have thought that it
> was an ideal candidate to show the advantages of on-disk representation
> (several low cardinality columns) - any ideas?

This should be an ideal candidate for an on-disk bitmap index. However, in
your test case, current implementation works better when you create a single
bitmap index for those three columns. That is,

  create index bitmaptest_012 on bitmaptest using bitmap(val0, val1, val2);

Then you should get much better query performance on your test query. This
is because the "AND" operations are done inside this single bitmap index,
while the "AND" operations in your test case are done by Tom Lane's bitmap
scan.

This is one limitation of current implementation. I am working on improving
this.

Best,
Jie